algebra

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in triangle ABC, the size of angle B is 5 times the size of angle A and the size of angle C is 9 degrees less than 4 times the size of angle A
Find the size of angle A

  • algebra -

    You can set up the equations as follows:
    B=5A
    C=4A-9
    A+B+C=180 (sum of angles of a triangle).
    and solve for A, B and C.

    However, you can easily solve it by substitution into the third equation:
    A+B+C=180
    A + 5A + 4A-9 = 180
    10A=189
    A=18.9
    With A known, you can then find the remaining angles by substitution into the first two equation.

  • algebra -

    The sum of the angles of a triangle are 180 degrees.

    Therefore:
    Let x = angle A
    5x = angle B
    4x - 9 = angle C

    Equation:
    x + 5x + 4x - 9 = 180

    Solve for x.

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